In order to check the effectiveness of medicine in an environment close to that in the living body, three-dimensional culturing, in which cells are cultured in three dimensions, has been conventionally performed. In such three-dimensional culturing, there is a known calibration method in which, in order to observe the culture conditions of a cell clump in which a plurality of cells are aggregated in three dimensions, the accuracy of estimating the volume of the cell clump from an image including the cell clump is improved (for example, see PTL 1).
The technique in PTL 1 is used to analyze the whole cell clump but is not used to analyze individual cells constituting the cell clump. In cell-based studies or drug screening, it is necessary to quantify the reactions of individual cells constituting a cell clump. In particular, among the cells constituting the cell clump, the reactions are different between inner-side cells and outer-side cells.